let myWm = new WeakMap()

class Fish {
  constructor(name) {
    myWm.set(this, {
      _fishbone: ['草鱼', '鲫鱼', '青鱼']
    })
    this.name = name
  }
  isBone() {
    return myWm.get(this)._fishbone.includes(this.name)
  }
}

let fish1 = new Fish('草鱼')
let fish2 = new Fish('鮰鱼')

console.log(fish1.isBone());
console.log(fish2.isBone());